ISC (idle speed control) valve

I diagnosed a problem on my 1990 Miata to the ISC valve. Looks like a simple part to replace...but wait! How about around $500 for a new one? This thing must employ precious metals; it's like buying a part for a Maserati.

This can't be the only one that failed. Has anyone else bit the bullet on this?

Ken

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KWS wrote:

Hi Ken, I helped another person on here a while back with the ISC valve on a 1990 model. Is this the valve that is located in the throttle body? I remember having trouble determining exactly which part it was, but I may have access to another one. $500.00 is insane, that is a big percentage of the blue book value of the entire car.

Do you have a picture of the valve by any chance?

Pat

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Thanks, Pat...that's very kind of you to offer.

I bit the bullet and ordered a new one. In the interest of perhaps helping someone else, I took images and posted them here:

http://pg.photos.yahoo.com/ph/fourdoorcat/album?.dir !58scd

The first three images are of the throttle body and ISC valve attached. The next two show the parts disconnected with the gasket placed between them. The last three are different views of the ISC valve.

Thanks much...

Ken

pws wrote:

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It's all part of the ongoing mfrs conspiracy to induce you to buy a new car.

"How about around $500 for a new one? "

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Generally, I have found the parts for my '90 Miata to be reasonably priced. I understand that rationale of charging a premium for replacement parts; part of it is certainly legit but you are correct to point out that some gouging exists.

The good news is that the Miata fails so rarely. So when it comes to shelling out a few shekels for a clutch slave cylinder or a rear brake caliper, it isn't all that tough to take.

Ken

Chuck wrote:

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Parts that are available from other than the car mfr tend to have reasonable prices. Parts that only the mfr has available are the parts that tend to be way overpriced.

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I would think one reason is that they are manufactured in small amounts. That drives the price up greatly, because design and tooling must be paid for by much smaller numbers and the lowest cost manufacturing methods are not economical at such series.

Leon

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What were the symptoms of the failure???

Roland

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The idle was too fast. It was OK when the engine was cold and would not settle down when hot. This was intermittent for a while, then it was consistent (idle fast when hot). This is one of the troubleshooting scenarios covered in the Workshop Manual.

There is a simple test for the ISC which is to remove the connector and re-install it. A "click" is supposed to result (it did not). Next step is to measure the resistance between the terminals. At nominal temperatures, it should read around 12 ohms. Mine reads infinite ohms (it's open).

There may be other symptoms of an ISC failure, but this is what happened to my car.

Ken

Roland Smith wrote:

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Follow up: Got the new ISC valve and installed it this evening. Idle problem is resolved; the beast is back.

Ken

KWS wrote:

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